The present invention relates to the cleaning of a substrate processing system. More specifically, the present invention relates to methods and apparatus for removing cleaning residues, created during substrate processing, from the interior surfaces of a processing chamber.
High-density integrated circuits, commonly termed VLSI devices, are typically formed on semiconductor substrates by subjecting the substrates to a number of processing steps. These steps include operations such as deposition, etching, sputtering and diffusion. In the production of a finished substrate, each of these operations serves a function such as applying, patterning and manipulating the characteristics of the various layers employed in the given technology.
One of the primary steps in fabricating modern semiconductor devices is forming a dielectric layer on a semiconductor substrate. As is well known, such a dielectric layer can be deposited by chemical vapor deposition (CVD). In a conventional thermal CVD process, reactive gases are supplied to the substrate surface where heat-induced chemical reactions (homogeneous or heterogeneous) take place to produce a desired film. In a conventional plasma process, a controlled plasma is formed to decompose and/or energize reactive species to produce the desired film. In general, reaction rates in thermal and plasma processes may be controlled by controlling one or more of the following: temperature, pressure, and reactant gas flow rate.
An important way to improve quality and overall efficiency in fabricating devices is to clean the chamber effectively and economically. With growing pressures on manufacturers to improve processing quality and overall efficiency, eliminating the total down-time in a multiple-step process without compromising the quality of the wafers has become increasingly important for saving both time and money. During processing, reactive gases released inside the processing chamber form layers such as silicon oxides or nitrides on the surface of a substrate being processed. Undesirable oxide deposition occurs elsewhere in the CVD apparatus, such as in the area between the gas mixing box and gas distribution manifold. Undesired oxide residues also may be deposited in or around the exhaust channel and the walls of the processing chamber during such processes. Over time, failure to clean the residue from the CVD apparatus often results in degraded, unreliable processes and defective substrates. Without frequent cleaning procedures, impurities from the residue built up in the CVD apparatus can migrate onto the substrate. The problem of impurities causing damage to the devices on the substrate is of particular concern with today's increasingly small device dimensions. Thus, CVD system maintenance is important for the smooth operation of substrate processing, as well as resulting in improved device yield and better product performance.
Frequently, periodic chamber cleanings between processing of every N wafers is desired to improve CVD system performance in producing high quality devices. Providing an efficient, non-damaging clean of the chamber and/or substrate is often able to enhance performance and quality of the devices produced. Two methods of cleaning a processing chamber are in situ cleaning (also known as dry-etch cleaning) and wet cleaning. In an in-situ cleaning operation, process gases are evacuated from the processing chamber and one or more cleaning process gases are introduced. Energy is then applied to promote a reaction between the gases and any residues which may have accumulated on the processing chamber's interior surfaces. Residues on the processing chamber's interior react with the cleaning process gases, forming gaseous by-products which are then exhausted from the processing chamber, along with unreacted portions of the cleaning process gases. The cleaning process is followed by the resumption of normal processing.
In contrast to an in situ cleaning procedure, in which the processing chamber remains sealed, a wet cleaning procedure is performed by breaking the processing chamber's vacuum seal and manually wiping down the chamber's interior surfaces. A wet cleaning procedure is normally performed to remove residues which are not entirely removed by the in situ cleaning process, and thus slowly accumulate over time. A solvent is sometimes used to dissolve these residues. Once cleaned, the processing chamber is sealed and normal processing is resumed.
Unfortunately, such cleaning operations affect a substrate processing system's throughput in a variety of ways. For example, system throughput is reduced by the time involved in performing cleaning operations. In an in situ cleaning process, time is spent evacuating process gases from, and introducing/evacuating the cleaning process gases into/from the processing chamber. Flow rates, radio frequency (RF) power levels, temperature, pressure, and other cleaning process conditions must also be reset to desired levels after the cleaning process is completed. When a wet clean is performed, opening the processing chamber and physically wiping the chamber's interior surfaces results in even more down-time because the process must subsequently be re-stabilized. It is thus desirable to reduce the frequency with which such cleaning operations are performed.
Additionally, frequent cleaning operations tend to increase wear on the processing chamber components. For example, in-situ cleaning is typically performed using fluoridated carbons (e.g., CF.sub.4, C.sub.2 F.sub.6 and the like) or similar fluorine-containing gases (e.g., NF.sub.3 and the like) due to their highly reactive nature. Unfortunately, exposure to plasmas created from such gases often causes the deterioration of processing chamber components. This increased wear can lead to component failure, thereby causing extended down-time, and adversely affecting processing system throughput.
The use of reactive gases in cleaning process chambers, however, also suffers from a further disadvantage. The same radicals which provide desirable cleaning characteristics may themselves cause the formation of residues. For example, the use of such gases can cause the accumulation of polymer residues, which also exhibit undesirable qualities. The addition of oxygen to the cleaning process gas may reduce the formation of such polymer residues. In particular, ozone or an oxygen/ozone mixture may provide the desired reduction in polymer formation while speeding the cleaning process, due to ozone's greater reactivity.
Another example of residues generated by cleaning gases are the cleaning residues often formed by the use of fluoridated compounds in certain cleaning processes. These compounds may react with the aluminum or anodized aluminum which makes up many of the standard processing chamber's components to form an aluminum fluoride residue on the interior surfaces of the chamber and the chamber's components. The reaction between the aluminum and the fluorine containing compounds often occurs because the residues within the processing chamber vary in thickness and therefore have different cleaning times. Thus, certain areas of the processing chamber's interior may become residue-free (i.e., exposed) before others, resulting in the formation of an aluminum fluoride residue on the exposed portions of the chamber's interior.
What is needed, therefore, are improved methods and apparatus for cleaning semiconductor process chambers. In particular, the cleaning methods and apparatus should be capable of removing the residues created during substrate processing operations, while reducing or eliminating the subsequent formation of cleaning residues such as polymers and aluminum fluoride.